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Active yogurt cultures are the bacteria that are added to milk in order to start the fermentation process that makes yogurt. They are believed to help with digestion in general and lactose intolerance in particular. There have also been claims that active yogurt cultures can reduce cholesterol, increase immunity to infection, and work as anticarcinogens.
Milk that is used to make yogurt is usually pasteurized first in order to remove harmful bacteria. Then healthy bacteria are mixed into the yogurt. These organisms ferment the milk, turning its sugars into lactic acid and altering the proteins in the milk so that they form a creamy, gelatinous texture.
The bacteria that make active yogurt cultures are usually Streptococcus thermophilus and Lactobacillus bulgaricus. There can also be several other kinds of safe active bacteria in yogurt. Bifidobacterium bifidus is another type of bacteria added to yogurt. It can further help digestion for people with lactose intolerance. The exact mix of bacteria varies, depending on the product.
Some types of yogurt are heat pasteurized in order to extend shelf life. As this kills the bacteria that were used to make the yogurt, these products do not have active yogurt cultures. Other yogurts may have active cultures, but in numbers too small to have a significant effect. Products covered in yogurt, such as pretzels and raisins, and products with yogurt as an ingredient, such as salad dressings, do not have active yogurt cultures.
In the United States, one easy way to find out if a brand of yogurt has active cultures is to check the package for a seal from the National Yogurt Association (NYA). As applying for the seal is voluntary, other brands without it may also have live cultures. The only major difference is that the presence of cultures has probably not been proven by an objective party.
Certified yogurt has a minimum of 100 million active cultures in each gram when it is made. Frozen yogurt needs 10 million cultures per gram. The seal is awarded when the company making the product has provided the NYA with a lab analysis that verifies the number of cultures per gram of yogurt.
Yogurt products with active cultures come in a wide array of varieties. For the diet conscious, there are low calorie, low fat, and non fat versions. There are also dessert style yogurts made in the texture of custards or with flavors such as chocolate. Drinkable yogurt can also have active cultures.